The long-term objective of this project is to understand the genetic and epigenetic mechanisms by which the tumor cell regulates the expression of its tumor-specific antigens. To accomplish this objective somatic genetic analysis is being used to study the number, dominance and nature of the genes controlling the expression of several model surface antigens. Antigenic variants of murine lymphomas are being used as the experimental system. During the coming year work will be continued on analysis of Thy-1-variants to define additional genes involved in Thy-1 biosynthesis. Regulation of Thy-1 expression will be studied in myeloma x lymphoma hybrids. Somatic genetic analysis will also be carried out on the TL system. BIBLIOGRAPHIC REFERENCES: Nicolson, G., J. Robbins, and R. Hyman (1976). Cell surface receptors and their dynamics on toxin-treated malignant cells. J. Supramol. Structure, 4, 15-26. Hyman, R., and V. Stallings (1976). Characterization of a TL negative variant of a homozygous TL positive mouse lymphoma. Immunogenetics, 3, 75-84.